Add {CancelableTaskManager} to handle {Cancelable} concurrent tasks.

src/cancelable-task.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/cancelable-task.h"
 
 #include "src/base/platform/platform.h"
 #include "src/isolate.h"
 
 namespace v8 {
 namespace internal {
 
 
-Cancelable::Cancelable(Isolate* isolate)
-    : isolate_(isolate), is_cancelled_(false) {
-  isolate->RegisterCancelableTask(this);
+Cancelable::Cancelable(CancelableTaskManager* parent)
+    : parent_(parent), status_(kWaiting), id_(0), cancel_counter_(0) {
+  id_ = parent->Register(this);
 }
 
 
 Cancelable::~Cancelable() {
-  if (!is_cancelled_) {
-    isolate_->RemoveCancelableTask(this);
+  // Idle tasks could still be in kWaiting. Avoid race with shutdown of isolate
+  // by moving the state to kRunning.
+  if (TryRun() || IsRunning()) {

[Hannes Payer (out of office), 2015/11/13 20:03:22]

Setting it to running here is a bit non-logical. Would it possible to abort it
in this case?

[Michael Lippautz, 2015/11/13 22:51:03]

Directly aborting is not possible, since the manager might have been destroyed
already. Changing to running avoids an additional state.

+    bool removed = parent_->TryAbort(id_);
+    USE(removed);
+    // This is counter intuitive but correct: Removing a task also involves
+    // canceling it, which is not possible anymore, since it is already in
+    // state running.
+    DCHECK(removed == false);
   }
 }
 
 
+static bool ComparePointers(void* ptr1, void* ptr2) { return ptr1 == ptr2; }
+
+
+CancelableTaskManager::CancelableTaskManager()
+    : task_id_counter_(0), cancelable_tasks_(ComparePointers) {}
+
+
+uint32_t CancelableTaskManager::Register(Cancelable* task) {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  uint32_t id = ++task_id_counter_;
+  // If the id is still in use, try to find a new one.

[Hannes Payer (out of office), 2015/11/13 20:03:22]

Just say that the while loop is used in the overflow case.

[Michael Lippautz, 2015/11/13 22:51:03]

Done.

+  while (cancelable_tasks_.Lookup(reinterpret_cast<void*>(id), id) != nullptr) {
+    ++id;
+  }
+  HashMap::Entry* entry =
+      cancelable_tasks_.LookupOrInsert(reinterpret_cast<void*>(id), id);
+  entry->value = task;
+  return id;
+}
+
+
+bool CancelableTaskManager::TryAbort(uint32_t id) {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  Cancelable* value = reinterpret_cast<Cancelable*>(
+      cancelable_tasks_.Remove(reinterpret_cast<void*>(id), id));
+  if (value != nullptr) {
+    bool success = value->Cancel();
+    cancelable_tasks_barrier_.NotifyOne();
+    if (!success) return false;
+    return true;
+  }
+  return false;
+}
+
+
+void CancelableTaskManager::CancelAndWait() {
+  // Clean up all cancelable fore- and background tasks. Tasks are canceled on
+  // the way if possible, i.e., if they have not started yet.  After each round
+  // of canceling we wait for the background tasks that have already been
+  // started.
+  base::LockGuard<base::Mutex> guard(&mutex_);
+
+  // HashMap does not support removing while iterating, hence keep a set of
+  // entries that are to be removed.
+  std::set<uint32_t> to_remove;
+
+  // Cancelable tasks could potentially register new tasks, requiring a loop
+  // here.
+  while (cancelable_tasks_.occupancy() > 0) {
+    for (HashMap::Entry* p = cancelable_tasks_.Start(); p != nullptr;
+         p = cancelable_tasks_.Next(p)) {
+      if (reinterpret_cast<Cancelable*>(p->value)->Cancel()) {
+        to_remove.insert(reinterpret_cast<Cancelable*>(p->value)->id());
+      }
+    }
+    // Remove tasks that were successfully canceled.
+    for (auto id : to_remove) {
+      cancelable_tasks_.Remove(reinterpret_cast<void*>(id), id);
+    }
+    to_remove.clear();
+
+    // Finally, wait for already running background tasks.
+    if (cancelable_tasks_.occupancy() > 0) {
+      cancelable_tasks_barrier_.Wait(&mutex_);
+    }
+  }
+}
+
+
+CancelableTask::CancelableTask(Isolate* isolate)
+    : Cancelable(isolate->cancelable_task_manager()), isolate_(isolate) {}
+
+CancelableIdleTask::CancelableIdleTask(Isolate* isolate)
+    : Cancelable(isolate->cancelable_task_manager()), isolate_(isolate) {}
+
 }  // namespace internal
 }  // namespace v8